In the well-known Darlington-connected transistor pair a driver transistor has its emitter connected to the base of an output transistor and the collectors are commonly connected. Since the driver acts as an emitter follower to drive the output transistor as a common emitter element, a very high current gain is achieved. This applies to both the NPN and PNP transistor versions that are popular in discrete and integrated-circuit (IC) forms. However, the Darlington pair has an undesirably high saturation voltage. When turned on the saturation state produces a voltage drop of V.sub.BE +V.sub.SAT which is approximately one volt at 300' K. This is high relative to the fractional volt saturation (V.sub.SAT) of a single common emitter transistor.
One way to overcome the problem is set forth in U.S. Pat. No. 4,542,389, which issued to Dennis M. Monticelli on Sept. 17, 1985. This patent is titled FEED FORWARD DARLINGTON CIRCUIT and is assigned to the assignee of the present invention. The Monticelli invention involves the inclusion of a complementary transistor in the Darlington-connected pair which acts to drive the output transistor into saturation when turned on. Thus, the pair will produce a saturation output equal to that of a single transistor. This action requires that the Darlington driver transistor have a low beta in the inverted state and this may require a specially constructed driver transistor. The teaching in U.S. Pat. No. 4,542,399 is incorporated herein by reference.